No, I haven’t. On the list for the next read, and with that I have received my first advanced Christmas present from someone for this year. Thanks! At the moment, I am re-reading The Journals of Captain Cook, as it is topical and a long, long while since I first read it. It is much more significant (and interesting, too) this time around.
23 October, 2017, 20:35 UTC, position; N 2º 3.89’ W 157º 4.74’, 8 leagues out from destination.
Last night I shortened sail before retiring for the night, to kill some of the way the vessel was making, or it would have sailed clear past Kritimati at 10.4 knots (avg) while I was asleep. I brought in the gennaker, set the jib in its place, and reefed down the main. There was some variation in the wind happening at the time, as it appeared to be veering, but a bit later settled to a gentle breeze, as per the Beaufort scale, 6 points to port off the stern, almost abeam. My way became 6.2 knots, and I was happy with that for the night (the screenie shows the earlier situation, with the wind still in the port quarter, and not making much way)…
It worked a treat, as this morning I found myself within 20 leagues of Kritimati. I furled in the jib and reset the sail area again to gennaker and full main, set it reasonably close hauled on the reach, with the wind still on a point abaft the port beam, and let the Ocean Belle heel triumphantly to starboard for her dash into Kritimati. This is an ideal situation for a fore and aft rigged vessel, and for the first time since I have had the sim, the Ocean Belle is making way a knot and a half faster that the wind is blowing.
Sea birds start to appear, and despite the fact that this has been a simulation I have been nursing through the voyage, there is some elation to be felt at the sight. It must be a wonderful feeling IRL!
I will be away IRL for three days as from tomorrow early morning, so I am going to heave to just north of Kritimati, haul in the sails and complete this leg of the voyage when I get back. I’m contemplating my diplomatic strategy with the unfriendly looking denizen of Kritimati @BeachAV8R so kindly warned me about!
Celestial Navigation, and others
(omit reading if the subject does not interest you at all, please)
I did get to the bottom of the issue of the time difference I was experiencing in the last post. This may be a little long winded to explain, not sure yet as I write it…
All my readings of sun zenith throughout the voyage have had an error with the actual UTC time of the sun over the meridian, yet are pinpointing me accurately (down to within 8-12 nautical miles, on some of them). I have been finding this very perplexing. I have never been satisfied with being right by chance, so I looked into it in some greater depth. In short, this is what is happening…
The simulation is calculating the sun’s apparent movement with the same error that I am including in my calculations, therefore giving me the correct longitude position in the game world, even though the real world times are quite different.
For example, yesterday, there was a 16 minute error on the real UTC time of the sun over meridian W 155º. The assumption of mine was that the sun would be over the Prime Meridian at exactly 12:00 UTC. It turns out that the game is making exactly the same assumption, and causing my calculations to work. But it is not correct.
There is a little feature of orbital mechanics for bodies with a rotational axis tilted to its plane of orbital rotation. It is exactly the same feature that tail-dragger pilots know about and that happens transitionally as you pick the tail up during the take off run (fond memories of the PA-18-150, for me). We know it as gyroscopic precession. I have heard about this feature before, but ignored its effects. Where the planet is concerned, this gyroscopic resultant has the effect of causing the rotation of the planet to lag and gain, back and forth, throughout the year, so the time of the sun over the Prime Meridian is, actually, rarely exactly 12:00 UTC.
With this in mind, I break out Stellarium (which is quite accurately modeled), and take snapshots of the time over the Prime Merdian on the dates of the Vernal Equinox, Vernal Solstice, Invernal Equinox, and Invernal Solstice. Here are the results…
Note the zenith times, which I was originally assuming to be 12:00 UTC.
March 20: UTC 12:06:55
June 21: UTC 12:01:30
September 22: UTC 11:52:10
December 21: UTC 11:57:55
The variation, on some points of the year, is even considerably greater than these, as like now, a 16 minute difference.
Again: This is an error that I made that coincided with an error in the game regarding sun time over the Prime Meridian. There is nothing wrong with the method of calculation, I stress, or it would never have been pinpointing my longitude with the accuracy with which it was doing so.
Add to this, an error that exists in the game, in which Polaris does not stay static over Geographic North, but behaves more like Kochab in Ursa Minor, and we have an astronomical model in Sailaway that is nowhere near as accurate as advertised. No wonder they are not giving us a sextant! However, benefit of the doubt; it is a brand new game, and fixing these issues may well be on the cards. I’ll continue to gather data, and when I have some more concrete stuff to put in writing to the developers, I’ll do so (if someone doesn’t beat me to it).
Now, who says you don’t learn new things on the Mudspike Christmas Expedition? It is why I’m such a fan of it! LOL!
@PaulRix You knew this all along and have been having a laugh at my expense!